In semiconductor processing, many operations may be performed on a single workpiece or semiconductor wafer. In many processing operations, a particular orientation of the workpiece and/or knowledge of the position of the workpiece with respect to a workpiece holder is needed in order to properly process or handle the workpiece. For example, operations such as an exchange of workpieces between transport carriers or storage cassettes and the processing system and a transfer of the workpieces from an atmospheric environment into an evacuated environment of a process chamber of the processing system through one or more load lock chambers may require specific orientation(s) or knowledge of the spatial position of the workpiece for proper workpiece handling and processing.
An orientation of the workpiece (e.g., notch alignment) may be performed within the evacuated environment or atmospheric environment via a light presence sensor, whereby a beam of light is emitted by a light emitter and directed toward the workpiece concurrent to a rotation of the workpiece with respect to the beam of light. A variation in light received by a light receiver can be then used to determine the position of a notch defined in the workpiece and/or an eccentricity of a position of the workpiece, depending on how the light is fully or partially received. One such system is disclosed in U.S. Pat. No. 5,740,034 to Hiroaki Saeki, whereby a waveform associated with the received light signals is utilized to determine the position of the notch and/or eccentric position of the workpiece.